Light emitting diode

ABSTRACT

A light emitting diode includes an insulating substrate, a first MgO layer, a semiconductor carbon nanotube layer, a second MgO layer, a functional dielectric layer, a first electrode, and a second electrode. The semiconductor carbon nanotube layer has a first surface and a second surface. The first MgO layer coats entire the first surface. The second surface is divided into a first region and a second region. The first region is coated with the second MgO layer. The second MgO layer is covered by the functional dielectric layer. The second region is exposed. The first electrode is electrically connected to the first region. The second electrode is electrically connected to the second region.

This application is a continuation application of U.S. patentapplication Ser. No. 14/983,613, filed on Dec. 30, 2015, entitled,“LIGHT EMITTING DIODE”, which claims all benefits accruing under 35U.S.C. §119 from China Patent Application No. 201410846889.5, filed onDec. 31, 2014 in the China Intellectual Property Office, the contents ofwhich are hereby incorporated by reference.

BACKGROUND

1. Technical Field

The present invention relates to a light emitting diode (LED).

2. Description of Related Art

LEDs are semiconductors that convert electrical energy into light.Compared to conventional light sources, LEDs have higher energyconversion efficiency, higher radiance (i.e., they emit a largerquantity of light per unit area), longer lifetime, higher responsespeed, and better reliability. LEDs also generate less heat. Therefore,LED modules are widely used as light sources in optical imaging systems,such as displays, projectors, and so on.

A typical LED commonly includes an N-type semiconductor layer, a P-typesemiconductor layer, an N-type electrode, and a P-type electrode. TheP-type electrode is located on the P-type semiconductor layer. TheN-type electrode is located on the N-type semiconductor layer.Typically, the P-type electrode is transparent. In operation, a positivevoltage and a negative voltage are applied respectively to the P-typesemiconductor layer and the N-type semiconductor layer. Thus, holes inthe P-type semiconductor layer and photons in the N-type semiconductorlayer can enter the active layer and combine with each other to emitvisible light. However, the material of the semiconductor layer isgallium arsenide, gallium phosphide, silicon carbide, or galliumnitride, thus an active layer is required to be located between theN-type semiconductor layer and the P-type semiconductor layer. Thestructure is complicate.

What is needed, therefore, is a light emitting diode that can overcomethe above-described shortcomings.

BRIEF DESCRIPTION OF THE DRAWINGS

Many aspects of the embodiments can be better understood with referencesto the following drawings. The components in the drawings are notnecessarily drawn to scale, the emphasis instead being placed uponclearly illustrating the principles of the embodiments. Moreover, in thedrawings, like reference numerals designate corresponding partsthroughout the several views.

FIG. 1 shows a cross-section view of one embodiment of an LED.

FIG. 2 shows a scanning electron microscope (SEM) view of asemiconductor carbon nanotube film.

FIG. 3 shows a cross-section view of one embodiment of an LED.

FIG. 4 shows a cross-section view of one embodiment of an LED.

DETAILED DESCRIPTION

The disclosure is illustrated by way of example and not by way oflimitation in the figures of the accompanying drawings in which likereferences indicate similar elements. It should be noted that referencesto “an” or “one” embodiment in this disclosure are not necessarily tothe same embodiment, and such references mean at least one.

Referring to FIG. 1, one embodiment of a light emitting diode (LED) 10comprises an insulating substrate 110, a semiconductor carbon nanotubelayer 120, an MgO layer 130, a functional dielectric layer 140, and afirst electrode 121, and a second electrode 122.

The semiconductor carbon nanotube layer 120, the MgO layer 130, and thefunctional dielectric layer 140 are stacked on the insulating substrate110, and the semiconductor carbon nanotube layer is in direct contactwith the insulating substrate 110. The MgO layer 130 is located on aportion of the semiconductor carbon nanotube layer 120. The functionaldielectric layer 140 is located on the MgO layer 130. The firstelectrode 121 and the second electrode 122 are electrically connected tothe semiconductor carbon nanotube layer 120.

A surface of the semiconductor carbon nanotube layer 120 between thefirst electrode 121 and the second electrode 122 defines a first portionand a second portion. The first portion is adjacent to the firstelectrode 121, and the second portion adjacent to the second electrode122. The first portion and the second portion are aligned side by sidealong a direction from the first electrode 121 to the second electrode122. The MgO layer 130 is located on the first portion, and the secondportion is exposed. The functional dielectric layer 140 is located onand covers the MgO layer 130.

The insulating substrate 110 is configured as a support. A material ofthe insulating substrate 110 can be hard material or flexible material.The hard material can be as glass, quartz, ceramics, or diamond. Theflexible material can be plastics or resins. The flexible material canalso be polyethylene terephthalate, polyethylene naphthalate,polyethylene terephthalate, or polyimide. In one embodiment, thematerial of the insulating substrate 110 is polyethylene terephthalate.The insulating substrate 110 is used to support the different elementson the insulating substrate 110.

The semiconductor carbon nanotube layer 120 is located on the insulatingsubstrate 110. The semiconductor carbon nanotube layer 120 comprises aplurality of carbon nanotubes. The semiconductor carbon nanotube layer120 has semi-conductive property. The semiconductor carbon nanotubelayer 120 can consist of a plurality of semi-conductive carbonnanotubes. In one embodiment, a few metallic carbon nanotubes can beexisted in the semiconductor carbon nanotube layer 120, but the metalliccarbon nanotubes cannot affect the semi-conductive property of thesemiconductor carbon nanotube layer 120.

The plurality of carbon nanotubes are connected with each other to forma conductive network. The carbon nanotubes of the semiconductor carbonnanotube layer 120 can be orderly arranged to form an ordered carbonnanotube structure or disorderly arranged to form a disordered carbonnanotube structure. The term ‘disordered carbon nanotube structure’includes, but is not limited to, a structure where the carbon nanotubesare arranged along many different directions, and the aligningdirections of the carbon nanotubes are random. The number of the carbonnanotubes arranged along each different direction can be substantiallythe same (e.g. uniformly disordered). The disordered carbon nanotubestructure can be isotropic. The carbon nanotubes in the disorderedcarbon nanotube structure can be entangled with each other. The term‘ordered carbon nanotube structure’ includes, but is not limited to, astructure where the carbon nanotubes are arranged in a consistentlysystematic manner, e.g., the carbon nanotubes are arranged approximatelyalong a same direction and/or have two or more sections within each ofwhich the carbon nanotubes are arranged approximately along a samedirection (different sections can have different directions).

In one embodiment, the carbon nanotubes in the semiconductor carbonnanotube layer 120 are arranged to extend along the directionsubstantially parallel to the surface of the carbon nanotube layer. Inone embodiment, all the carbon nanotubes in the semiconductor carbonnanotube layer 120 are arranged to extend along the same direction. Inanother embodiment, some of the carbon nanotubes in the carbon nanotubelayer are arranged to extend along a first direction, and some of thecarbon nanotubes in the semiconductor carbon nanotube layer 120 arearranged to extend along a second direction, perpendicular to the firstdirection.

In one embodiment, the semiconductor carbon nanotube layer 120 is afree-standing structure and can be drawn from a carbon nanotube array.The term “free-standing structure” means that the semiconductor carbonnanotube layer 120 can sustain the weight of itself when it is hoistedby a portion thereof without any significant damage to its structuralintegrity. Thus, the semiconductor carbon nanotube layer 120 can besuspended by two spaced supports. The free-standing semiconductor carbonnanotube layer 120 can be laid on the insulating layer 104 directly andeasily. In one embodiment, the semiconductor carbon nanotube layer 120can be formed on a surface of insulated support (not shown).

The semiconductor carbon nanotube layer 120 can be a substantially purestructure of the carbon nanotubes, with few impurities and chemicalfunctional groups. The semiconductor carbon nanotube layer 120 can alsobe composed of a combination of semi-conductive and metallic carbonnanotubes obtained via chemical vapor deposition. The ratio betweensemi-conductive and metallic of carbon nanotubes is 2:1, and thepercentage of the semi-conductive carbon nanotubes is about 66.7% in thecombination. In one embodiment, all of the metallic carbon nanotubes canbe completely removed via chemical separation method. In anotherembodiment, most of the metallic carbon nanotubes are removed, and thereare a few metallic carbon nanotubes left. Furthermore, the percentage ofthe semi-conductive carbon nanotubes in the semiconductor carbonnanotube layer 120 ranges from about 90% to about 100%. Thesemiconductor carbon nanotube layer 120 has good semi-conductiveproperty. In one embodiment, the semiconductor carbon nanotube layer 120consists of a plurality of single-walled carbon nanotubes. The pluralityof single-walled carbon nanotubes are parallel with each other. Adiameter of the carbon nanotube is smaller than 2 nanometers. Athickness of the semiconductor carbon nanotube layer 120 ranges fromabout 0.5 nanometers to about 2 nanometers. A length of the carbonnanotube ranges from about 2 micrometers to about 4 micrometers. In oneembodiment, a diameter of the carbon nanotube is greater than 0.9nanometers and smaller than 1.4 nanometers.

Referring to FIG. 2, in one embodiment, the semiconductor carbonnanotube layer 120 consists of the single-walled carbon nanotubes, andthe percentage of the semi-conductive carbon nanotubes in thesemiconductor carbon nanotube layer 120 is about 98%. The plurality ofsingle-walled carbon nanotubes are entangled with each other to form theconductive network. The diameter of the single-walled carbon nanotube isabout 1.2 nanometers. The thickness of the semiconductor carbon nanotubelayer 120 is about 1.2 nanometers.

The semiconductor carbon nanotube layer 120 comprises a first surfaceand a second surface opposite to the first surface. The first surface isin direct contact with the insulating substrate 110, and the MgO layeris located on the second surface. At least 50% of the second surface iscovered by the MgO layer 130. The second surface is separated into thefirst portion and the second portion. The MgO layer 130 and thefunctional dielectric layer 140 are stacked on the first portion, andthe second portion is exposed to the air.

Furthermore, the MgO layer 130 can shield a half of the second surface.The MgO layer 130 is in direct contact with the semiconductor carbonnanotube layer 120. The MgO layer 130 is configured to modulate thefirst portion of the semiconductor carbon nanotube layer 120, reduceholes, and improve electrons in the first portion of the semiconductorcarbon nanotube layer 120. A thickness of the MgO layer 130 can rangefrom about 1 nanometer to about 15 nanometers. In one embodiment, thethickness of the MgO layer 130 ranges from about 1 nanometers to about10 nanometers. While the thickness of the MgO layer 130 is smaller than1 nanometer, the MgO layer 130 cannot effectively isolated the air andwater molecular from the semiconductor carbon nanotube layer 120, andthe structure of LED cannot sustain the stability; while the thicknessof the MgO layer 130 is greater than 15 nanometers, the holes in thesemiconductor carbon nanotube layer 120 cannot be effectively reduced,and the efficiency of LED will be dramatically reduced. In oneembodiment, the thickness of the MgO layer 130 is about 1 nanometer.

The functional dielectric layer 140 is located on the MgO layer 130. Inone embodiment, the functional dielectric layer 140 covers entire theMgO layer 130. The term “functional dielectric layer” means that thefunctional dielectric layer 140 can dope the semiconductor carbonnanotube layer 120 under the affect of the MgO layer 130. Furthermore,the functional dielectric layer 140 is insulating and can isolate thesemiconductor carbon nanotube layer 120 from oxygen and water molecular.Thus the semiconductor carbon nanotube layer 120 has N-type property. Amaterial of the functional dielectric layer 140 can be aluminum oxide,hafnium oxide, or yttrium oxide.

In addition, the functional dielectric layer 140 has high density, thusthe functional dielectric layer 140 can isolate the air and the watermolecular. Furthermore, the functional dielectric layer 140 lackspositive charges, thus the semiconductor carbon nanotube layer 120 canbe doped with electrons, and the semiconductor carbon nanotube layer 120has N-type property. A thickness of the functional dielectric layer 140can range from about 20 nanometers to about 40 nanometers. In oneembodiment, the thickness of the functional dielectric layer 140 rangesfrom about 25 nanometers to about 30 nanometers. While the thickness ofthe functional dielectric layer 140 is too small, such as smaller than20 nanometer, the functional dielectric layer 140 cannot isolate the airand water molecular. In one embodiment, the material of the functionaldielectric layer 140 is aluminum oxide, and the thickness is about 30nanometers.

The first electrode 121 and the second electrode 122 are spaced fromeach other. The material of the first electrode 121 and the secondelectrode 122 can be metal, alloy, indium tin oxide (ITO), antimony tinoxide (ATO), silver paste, conductive polymer, or metallic carbonnanotubes. The metal or alloy can be aluminum (Al), copper (Cu),tungsten (W), molybdenum (Mo), gold (Au), titanium (Ti), neodymium (Nd),palladium (Pd), cesium (Cs), scandium (Sc), hafnium (Hf), potassium (K),sodium (Na), lithium (Li), nickel (Ni), rhodium (Rh), or platinum (Pt),and combinations of the above-mentioned metal. In one embodiment, thematerial of the first electrode 121 and the second electrode 122 cancomprises Au and Ti. The thickness of the Ti is about 2 nanometers, andthe thickness of the Au is about 50 nanometers.

The first portion of the semiconductor carbon nanotube layer 120 has theN-type property, and the exposed second portion of the semiconductorcarbon nanotube layer 120 has P-type property. In use, first portion andthe second portion forms the P-N junction. While a positive voltage isapplied on the P-N junction, the electrons in the first portion willflow toward the second portion, and the holes in the second portion willbe injected into the first portion. The holes and the electrons will berecombined to emit light in the semiconductor carbon nanotube layer 120.

The LED has following advantages. The first portion of the semiconductorcarbon nanotube layer is coated with the MgO layer and the functionaldielectric layer, the function dielectric layer has high density andlack of positive charges, thus the function dielectric layer can provideelectrons for the first portion. Then the first portion has great N-typeproperty. The semiconductor carbon nanotube layer is configured as boththe N-type semiconductor layer and P-type semiconductor layer, thus thestructure of LED is simplified.

Referring to FIG. 3, one embodiment of a light emitting diode (LED) 20comprises an insulating substrate 110, a first MgO layer 150, asemiconductor carbon nanotube layer 120, a second MgO layer 130, afunctional dielectric layer 140, and a first electrode 121, and a secondelectrode 122. The first MgO layer 150 is sandwiched between thesemiconductor carbon nanotube layer 120 and the insulating substrate110, and in direct contact with the semiconductor carbon nanotube layer120.

The structure of the LED 20 is similar to the structure of LED 10,except that the LED 20 further comprises the first MgO layer 150sandwiched between the semiconductor carbon nanotube layer 120 and theinsulating substrate 110.

The semiconductor carbon nanotube layer 120 comprises a first surfaceand a second surface opposite to the first surface. The first surfacecan be coated with the first MgO layer 150. Furthermore, entire thefirst surface is coated with the first MgO layer 150. Thus a portion ofthe semiconductor carbon nanotube layer 120 is sandwiched between thefirst MgO layer 150 and the second MgO layer 130.

Referring to FIG. 4, one embodiment of a light emitting diode (LED) 30comprises an insulating substrate 110, an MgO layer 130, a semiconductorcarbon nanotube layer 120, a functional dielectric layer 140, and afirst electrode 121, and a second electrode 122. The semiconductorcarbon nanotube layer 120 is sandwiched between the MgO layer 130 andthe functional dielectric layer 140.

The structure of the LED 30 is similar to the structure of LED 10,except that the semiconductor carbon nanotube layer 120 is sandwichedbetween the MgO layer 130 and the functional dielectric layer 140. Thesemiconductor carbon nanotube layer 120 comprises a first surface and asecond surface. The MgO layer 130 is coated on entire the first surfaceof the semiconductor carbon nanotube layer 120. The second surfacedefines a first portion and a second portion. The functional dielectriclayer 140 is located on the first portion of the semiconductor carbonnanotube layer 120, and in direct contact with the semiconductor carbonnanotube layer 120. The second portion is exposed.

Depending on the embodiments, certain of the steps described may beremoved, others may be added, and the sequence of steps may be altered.It is also to be understood that the description and the claims drawn toa method may include some indication in reference to certain steps.However, the indication used is only to be viewed for identificationpurposes and not as a suggestion as to an order for the steps.

It is to be understood, however, that even though numerouscharacteristics and advantages of the present embodiments have been setforth in the foregoing description, together with details of thestructures and functions of the embodiments, the disclosure isillustrative only, and changes may be made in detail, especially inmatters of shape, size, and arrangement of parts within the principlesof the disclosure.

What is claimed is:
 1. A light emitting diode, comprising: an insulatingsubstrate; a first MgO layer located on the insulating substrate; asemiconductor carbon nanotube layer located on the first MgO layer,wherein the semiconductor carbon nanotube layer comprises a firstsurface and a second surface that is opposite to the first surface, andthe first surface is coated by the first MgO layer; a second MgO layerlocated on the second surface; wherein the second surface comprises afirst region and a second region, the first region is coated with thesecond MgO layer, and the second region is exposed; a functionaldielectric layer located on the second MgO layer; a first electrodeelectrically connected to the first region; and a second electrodeelectrically connected to the second region.
 2. The light emitting diodeof claim 1, wherein the first MgO layer is sandwiched between theinsulating substrate and the semiconductor carbon nanotube layer.
 3. Thelight emitting diode of claim 1, wherein the first MgO layer is indirect contact with the semiconductor carbon nanotube layer.
 4. Thelight emitting diode of claim 1, wherein the functional dielectric layerentirely covers the second MgO layer.
 5. The light emitting diode ofclaim 1, wherein the second MgO layer is in direct contact with thefirst region.
 6. The light emitting diode of claim 1, wherein the secondMgO layer and the functional dielectric layer are stacked on the firstregion.
 7. The light emitting diode of claim 1, wherein a thickness ofeach of the first MgO layer and the second MgO layer is range from about1 nanometer to about 15 nanometers.
 8. The light emitting diode of claim1, wherein the semiconductor carbon nanotube layer comprises a pluralityof carbon nanotubes.
 9. The light emitting diode of claim 1, wherein thesemiconductor carbon nanotube layer comprises a plurality ofsemi-conductive carbon nanotubes connected with each other to form anetwork structure.
 10. The light emitting diode of claim 9, wherein apercentage of the plurality of semi-conductive carbon nanotubes in thesemiconductor carbon nanotube layer is greater than or equal to 66.7%.11. The light emitting diode of claim 1, wherein the semiconductorcarbon nanotube layer consists of a plurality of semi-conductive carbonnanotubes.
 12. The light emitting diode of claim 1, wherein a thicknessof the semiconductor carbon nanotube layer ranges from about 0.5nanometers to about 2 nanometers.
 13. The light emitting diode of claim1, wherein a material of the functional dielectric layer is selectedfrom the group consisting of aluminum oxide, hafnium oxide, and yttriumoxide.
 14. The light emitting diode of claim 1, wherein a thickness ofthe functional dielectric layer ranges from about 20 nanometers to about40 nanometers.
 15. The light emitting diode of claim 1, wherein thesemiconductor carbon nanotube layer is a free-standing structure.